'\" t
.\"     Title: CREATE EVENT TRIGGER
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 2021
.\"    Manual: PostgreSQL 13.3 Documentation
.\"    Source: PostgreSQL 13.3
.\"  Language: English
.\"
.TH "CREATE EVENT TRIGGER" "7" "2021" "PostgreSQL 13.3" "PostgreSQL 13.3 Documentation"
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.SH "NAME"
CREATE_EVENT_TRIGGER \- define a new event trigger
.SH "SYNOPSIS"
.sp
.nf
CREATE EVENT TRIGGER \fIname\fR
    ON \fIevent\fR
    [ WHEN \fIfilter_variable\fR IN (filter_value [, \&.\&.\&. ]) [ AND \&.\&.\&. ] ]
    EXECUTE { FUNCTION | PROCEDURE } \fIfunction_name\fR()
.fi
.SH "DESCRIPTION"
.PP
\fBCREATE EVENT TRIGGER\fR
creates a new event trigger\&. Whenever the designated event occurs and the
WHEN
condition associated with the trigger, if any, is satisfied, the trigger function will be executed\&. For a general introduction to event triggers, see
Chapter\ \&39\&. The user who creates an event trigger becomes its owner\&.
.SH "PARAMETERS"
.PP
\fIname\fR
.RS 4
The name to give the new trigger\&. This name must be unique within the database\&.
.RE
.PP
\fIevent\fR
.RS 4
The name of the event that triggers a call to the given function\&. See
Section\ \&39.1
for more information on event names\&.
.RE
.PP
\fIfilter_variable\fR
.RS 4
The name of a variable used to filter events\&. This makes it possible to restrict the firing of the trigger to a subset of the cases in which it is supported\&. Currently the only supported
\fIfilter_variable\fR
is
TAG\&.
.RE
.PP
\fIfilter_value\fR
.RS 4
A list of values for the associated
\fIfilter_variable\fR
for which the trigger should fire\&. For
TAG, this means a list of command tags (e\&.g\&.,
\*(AqDROP FUNCTION\*(Aq)\&.
.RE
.PP
\fIfunction_name\fR
.RS 4
A user\-supplied function that is declared as taking no argument and returning type
event_trigger\&.
.sp
In the syntax of
CREATE EVENT TRIGGER, the keywords
FUNCTION
and
PROCEDURE
are equivalent, but the referenced function must in any case be a function, not a procedure\&. The use of the keyword
PROCEDURE
here is historical and deprecated\&.
.RE
.SH "NOTES"
.PP
Only superusers can create event triggers\&.
.PP
Event triggers are disabled in single\-user mode (see
\fBpostgres\fR(1))\&. If an erroneous event trigger disables the database so much that you can\*(Aqt even drop the trigger, restart in single\-user mode and you\*(Aqll be able to do that\&.
.SH "EXAMPLES"
.PP
Forbid the execution of any
DDL
command:
.sp
.if n \{\
.RS 4
.\}
.nf
CREATE OR REPLACE FUNCTION abort_any_command()
  RETURNS event_trigger
 LANGUAGE plpgsql
  AS $$
BEGIN
  RAISE EXCEPTION \*(Aqcommand % is disabled\*(Aq, tg_tag;
END;
$$;

CREATE EVENT TRIGGER abort_ddl ON ddl_command_start
   EXECUTE FUNCTION abort_any_command();
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
There is no
\fBCREATE EVENT TRIGGER\fR
statement in the SQL standard\&.
.SH "SEE ALSO"
ALTER EVENT TRIGGER (\fBALTER_EVENT_TRIGGER\fR(7)), DROP EVENT TRIGGER (\fBDROP_EVENT_TRIGGER\fR(7)), CREATE FUNCTION (\fBCREATE_FUNCTION\fR(7))
